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dcfcends from an angle, as in the figure, fo 
that it is obliged to fall into the vertex of the 
angle, and moreover it paffes over a point A, 
with which it is made to correfpond, by the 
help of a microfcope. It is a pity that Mr. 
Siffon negledted fo effential a circumftance 
in your fedtor, but that is not your fault. The fedtor, 
with which M. de la Caille made all his oblervations, 
and which is come into my hands fince his death, 
has a fine needle at the center, from which the filver 
wire is fufpended by a loop, thus ------- 
M. Pingre, who is returned from the ifland 
of Rodrigues, has found the parallax of the fun 
to be the fame as I have done, namely 9" Jl. I 
am not furprifed that you find it to be only 8 
fince the Swedifh obfervations, which appear to me 
to be very good, make it hill lefs than you have 
found it. Thefe uncertainties arife from our not hav- 
ing the difference of the meridians of the Cape, Rod- 
rigues, Tobolfki, Paris, and London well determined. 
You are therefore quite right to colledt together the 
obfervations of Jupiter’s Satellites, which will ferve 
to land thefe longitudes. I thank you for thofe which 
you have fent me, and I have hereto added thofe of 
the fir ft fatellite which were made at Paris in 1761, 
for one can fcarce employ any but thefe for this pur- 
pofe. 
On the 19th of July 1763 we fhall have an oc- 
cupation of antares by the Moon, on the 2d of 
November an occupation of Mars, on the 8th of Sep- 
tember one of mercury : they will be very proper for 
determining the difference of longitude between Lon- 
don and Paris. In 1764 there will be a hill greater 
I number. 
